Particles trapped in fluid-liquid interfaces interact with each other via lateral capillary forces that arise because of their weight, and when present also by other forces such as electrostatic forces, to form monolayer arrangements. Particles are able to float at the interface because of the vertical capillary forces that arise due to the deformation of the interface. If the interface did not deform, the vertical capillary forces will be zero and the particles will not be able to float on the surface. But, this also results in lateral capillary forces. A common example of capillarity-driven self-assembly is the clustering of breakfast-cereal flakes floating on the surface of milk. The deformation of the interface by the flakes gives rise to lateral capillary forces which cause them to cluster. In recent years, many studies have been conducted to understand this behavior of trapped particles because of their importance in a range of physical applications and biological processes, e.g., formation of pollen and insect egg rafts, self-assembly of particles at fluid-fluid interfaces resulting in novel nano-structured materials, stabilization of emulsions, and the formation anti-reflection coatings for high-efficiency solar cells, photonic crystals and biosensor arrays. Capillarity-driven self-assembly, however, produces monolayers which have defects and lack long-range order, and for monolayers containing two or more different types of particles the technique does not allow for any control of the particle-scale structure as capillary forces simply cause particles to cluster.